Directive antenna



June 26, 1951 A. M. CASABONA 2,557,941

E DIRECTIVE ANTENNA Filed July 7, 1945 v s Sheets-Sheet 1 ATYURNEY June26, 1951 CASABQNA 2,557,941

DIRECTIVE ANTENNA Filed July 7, 1945 s She eis-Sheet 2 ATTORNEY June 26,1951 CASABONA 2,557,941

DIRECTIVE ANTENNA Filed July 7, 1945 's Shets-Sheet s IN VEN TOR. 45ANTHONY M. C/isflam/A NY m ATTORNEY Patented June 26, 1951 DIRECTIVEANTENNA Anthony M. Casabona, New York, N. Y., assignor to FederalTelephone and Radio Corporation, New York, N. Y., a corporation ofDelaware Application July 7, 1945, Serial No. 603,688

4 Claims.

This invention relates to composite antennas and more particularly todirective antenna systems of a type dependent upon the resultant fieldradiation produced by directly energized antenna arrays in combinationwith parasitically energized antenna array or reflectors.

' In certain cases a sharply directive pattern of relatively smallazimuth angle is desired having relatively high front-to-back ratio. Ifthe parasitic members of the array constituting the reflectors are tunedto maximum reflection, the propagated signal is radiated in a desireddirection having a horizontal and vertical directivity. In such a systemthe power output requirements of the transmitter are low and at the sametime interaction between the directive antennas and other nearbyantennas is eliminated. However, in order to insure maximum efficiencyin such a system the antenna array must be constructed so as toeliminate any possibility of detuning due to changes in electricalcharacteristics. A rigid form of construction thus prevents undesirablevariation in characteristics except those encountered when the array issubjected to accumulations of ice or snow on the radiating members. Anantenna array utilizing a reflector varies in radiation resistanceaccording to the spacing between the fed radiator and reflector. Thisproperty is useful in matching the array to feeder lines. The dimensionsof the array can be established from known formulas one of which Iinclude to compute the dimensions of a dipole array operative over arequired frequency band (having a desired horizontal radiation pattern),and which will produce zero signal 40 from the azimuth angle at whichmaximum signal is obtained.

Having designed an antenna of the type above mentioned, its pattern maystill be subject to some change due to various causes such as theweather conditions above mentioned. In order to maintain constant such apattern, it is necessary to provide those features in the structurewhich will tend to minimize or prevent changes in the pattern arisingfrom the physical conditions mentioned, or other causes.

It is an object of my invention to provide an antenna array having ahigh front-to-back ratio with the major lobe sensed in such a manner asto produce and maintain a horizontal pattern of zero signal a smallnumber of degrees from the azimuth angle at which maximum signal isobtained.

It is a further object of my invention to provide an antenna arrayincorporating certain improvements in construction so as toprovide arigid assembly which will prevent and eliminate variations of electricalcharacteristics due to changes in dimensions, variations in separationof constituting members of the array, or fragile design.

It is still a further object of my invention to provide an antenna arrayelectrically designed and assembled so as to render negligible thelosses in radiation power due to the accumulation of ice or snow on theexposed portions of the array which form the radiating surfaces.

It is an additional object of my invention to provide an antenna arrayelectrically designed and assembled so as to reduce the detuning efi'ectof any accumulation of ice or snow on the radiating members of theantenna or on the junction points of the radiating members with theirrespective supporting systems.

Still another object of my invention is to provide an antenna assemblyso designed as to possess a lumped capacity of relatively high value atthe fed ends of each dipole thereby allowing matching stubs and shortingbars to be of compact size, contributing to the small size necessary forthe enclosing shield around the ends of each dipole, the matching stubs,and shorting bars.

According to a feature of my invention, I provide an antenna consistingof four dipole antennas two of which are fed and are spacedsubstantially electrical degrees,

apart in the vertical plane while the alternate dipoles are utilized asreflectors, being spaced apart in a vertical plane an equivalent numberof degrees and also being spaced behind the fed membersv or mainradiators a predetermined amount, and tuned in such a manner as to ive ahigh front-to-back ratio. The vertical spacing of 180 electrical degreesprovides for minimum radiation above and below the array, and, as may beconcluded, the combination of horizontal and vertical directivity allowsfor maximum directive radiation usinga minimum of power.

The antenna units are supported at their innermost ends by two shieldboxes, and are electrically insulated from these shield boxes byinsulating bushings or suitable low loss material. The dipoles beingcenter fed allows for a form of construction in which the inner end ofabout two inches of each antenna rod is enclosed in a shield box. Thisportion of each rod thereforedoes not radiate but contributes to theestablishment of a large lumped capacity between the two antenna 'shieldbox.

As an illustrative instance, according to a feature of my invention, thedesired radiation pattern for a specific application was secured byutilizing known formulas and the general equation determining thehorizontal pattern of a dipole of any length 2L:

sine (l sine ][sine +sine 0?] COS 0 where L is one-half of the totallength of the dipole. Using this equation it is possible to compute thesize of a dipole which will produce zero signal 40 degrees from theazimuth angle at which maximum signal is obtained. The total length 2Lof the dipole is found to be 440 degrees. By reducing the spacingbetween the fed radiator and reflectors from approximately -9()electrical degrees to 35 electrical degrees a point will be reached atwhich the maximum front-toback ratio is obtained, while the reflectorstubs are tuned to assist in obtaining'this front-toback ratio. Thefed-radiator stubs are tuned to match the line impedance.

In this manner a directive, sharp pattern was secured as the signalincreased from zero to maximum in 40 degrees azimuth angle.

Abetter understanding of my invention and the objects and featuresthereof may be had by referring to the accompanying drawings, in which:

Fig. 1 is a front view in partial section;

Fig. 2 is a side view in partial section;

Fig. 3 is a top plan view of the uppermost shield box A with the coverremoved; and

Fig. 4 is a bottom plan view of the lower'box B with the cover removed.

Turning first to Fig. 1 there is shown generally the central portion ofthe directive antenna array in which directly fed dipole antennaelements I, 2 and 3, 4 are shown mounted in shield boxes 5, 5 which aremade of conductive material.

Likewise, parasitically fed dipole antenna ele-- ments 1, 8 and 9, itare spaced approximately 35 behind the directly fed dipoles in the sameshield boxes 5, 6, as shown in Fig. 2. Each antenna element is supportedin and insulated from the shield box by insulated bushings ll secured toshield box by screws l2. As may be seen from the view of shield box 5,the inter-- mediate ends of the antenna elements such as I and 2 arebrought closely together to effect a high degree of capacitive coupling.Terminals f 3 are placed on the endof each element to effect electricalconnection to a transmission line l4, preferably of shielded dual beadedline, as well as being the junction points of short tuning stubs l5adjustably tuned by means of shorting bars IS. The transmission line 14electrically interconnects antenna elements I, 2 only, thereby enablingthem to be energized to act as radiators. Similar connections existinside shield box 6, with antenna elements 3, 4 being energized throughtransmission line (4. Midway the length of transmission line 24 thereare feed line terminals ll for connection to feed line l8 which extendsvertically downward iromjunction box 19 directly through the center ofshield box 6, terminating in a screw-capped coupling unit 26 forconnection to a line of any length. Shield boxes 5 and 6 are arrangedvertically one above the other, and spaced apart in such a manner thatthe spacing between the contained dipoles shall be substantially ahalf-wavelength at the operating frequency. Enclosing beaded line H aretwo sections of tubing 2i and 22 joined together by junction box l9,with their flanged ends 23 fastened to shield boxes 5 and 6 by screws24. A length of tubing 25 encloses feed line 18 between junction box [9and lower shield box 6. These tubular sections add strength and rigidityto the array, as well as ensuring weatherproof electrical connections.To enable electrical connections to be made, shield boxes 5 and 6 areprovided with covers 26, 27 and sealing gaskets 28, 29, the covers beingheld in place by screws 30. The antenna elements I, 2, 3, 4 and i, 8, 9,It, are of equal length, each being approximately 220 in length. Whenmounted, the distance between their ends is approximately 440, thislength being determined by formula to produce a desired pattern.

Mounted 90 from the ends of the antenna elements and rigidly spacing theparasitic element from the fed element are low loss dielectric spacers3|, as shown in Figs. 3 and 4. The spacers consist of two rectangularportions 32 and 33 held tightly clamped to the antenna element by meanssuch as bolts 34, lock washers 35, and hex nuts 36. In this manner aspacing approximating 35 between adjacent elements is maintained.

As may be seen best in Fig. 2, 'the tuning stubs and shorting bars forthe parasitic antennas 'l, 8 and 9, it] are contained within tubularsections 31 and 38, mounted on shield boxes 5, 6 at their flanged ends39 and 40 by screws M. In order to further strengthen the array,supporting struts 42 are fastened to the back of shield boxes 5, 6 bymeans such as screws 43 and lock washers 44. Adjustable clamps 45 arefastened to these supporting struts by bolts 46 and clamping plates 41,for mounting the entire array on a pole or mast.

As will be seen, the proximity of the intermediate ends of the antennaelements within the shield boxes serves to increase capacitive couang;In addition, the enclosed portions of each element lies adjacent to aportion of the shield box, thereby affording more capacitive coupling,resulting in a high degree of lumped capacity at this point. Thisenablesrelatively short tuning stubs to be used, affording compactdesign.

As is well known in the art, the best receiving antenna is awell-designed efiicient transmitting antenna. While I have described myinvention primarily as a transmitting array, it is clear that the samemay be used as a receiving array of maximum efficiency at the operatingfrequency.

While I have disclosed as a particular embodiment of this invention apossible structural example, many variations in the detail and assemblythereof may be had without departing from my invention. It should beunderstood that this specific example is made merely by way ofexample,'and is not intended as a limitation on my invention asset'forth in the objects thereof and the attached claims.

I claim:

l.-A directiveantenna system comprising a pair of component antennasspaced thirty-five electrical degrees with respect to the operatingfrequency in the horizontal plane, one of said antennas forming a dipoleenergized to act as a primary radiator, transmission line means forenergizing said dipole, the other antenna acting as a parasitic dipoleor reflector, conductive shielding and supporting means enclosing thecentral portions of each dipole, insulatedly supporting and aligningsaid dipole antennas, and effecting substantial capacitive couplingbetween said central portions and said shielding means adjustable tuningmeans for said dipole antennas within said shielding means for tuningthe energized dipole to present a matched impedance to the line,corresponding tuning means connected between the adjacent ends of theparasitic dipole to secure a maximum front-to-back ratio of reflection,said shielding means effectively preventing radiation from andincreasing lumped capacity between the central portions of said pair ofdipole antennas, the lumped capacity at this point offsetting thedetuning elTect of any small additional amount of capacity that mayoccur external to said shielding means.

2. A directive antenna system comprising four dipole antennas arrangedin pairs, conductive shielding means for the central portion of eachpair of said dipoles, said dipoles being insulatedly supportedand'shielded over a predetermined length of said central portion by saidconductive shielding means whereby substantial capacitive coupling isefiected between said central portion and said shielding means, saidantennas being spaced to effectively produce a rectangular array,transmission means electrically interconnecting two of said dipoleslying in the same vertical plane for applying energy to said dipoles forradiation, a feed line coupled to said transmission means, tuning meansto tune said dipoles to present a matched impedance to said feed line,and other tuning means for tuning the remaining two dipoles toeffectively secure maximum front to back radiation ratio.

3. A directive antenna system adapted for operation at a givenwavelength comprising four dipole antennas arranged in pairs, conductiveshielding means for the central portion of each pair of said dipoles,said dipoles being insulatedly supported and shielded over apredetermined length of said central portion by said conductiveshielding means, units of said conductive shielding means being spacedone hundred and eighty electrical degrees at said operating frequencyapart in the vertical plane, the dipoles of each pair being spacedsubstantially thirty-five electrical degrees at said operating frequencyapart in the horizontal plane thereby effectively producing an array ofrectangular shape, transmission means electrically interconnecting twoof said dipoles lying in the same vertical plane for applying energy tosaid dipoles for radiation, a feed line coupled to said transmissionmeans, tuning means to tune said dipoles to present a matched impedanceto said feed line, and other tuning means for tuning the remaining twodipoles to effectively secure maximum front-to-back radiation ratio.

4. A directive antenna system comprising a plurality of dipole antennassubstantially arranged to define a rectangular solid being spaced in thevertical plane and in the horizontal plane, said dipole antennas formingan array having two dipoles energized to act as radiators, transmissionline means for energizing said dipoles, said array having two dipolesacting as parasitic elements or reflectors, conductive shielding andsupporting means enclosing the central portions of each pair ofhorizontally spaced dipoles insulatedly supporting and aligning saiddipole antennas and effecting substantial capacitive coupling betweensaid dipole antennas and said shielding means, adjustable tuning meansfor said pair of said dipole antennas within said shielding means fortuning the energized dipoles to present a matched impedance to the line,corresponding tuning means for tuning the parasitic dipoles to secure amaximum front-to-back ratio of reflection, said shielding meanseffectively preventing radiation from and increasing lumped capacitybetween the central portions of said pair of dipole antennas, the lumpedcapacity at this point offsetting the detuning effect of any smalladditional amount of capacity that may occur external to said shieldingmeans.

ANTHONY M. CASABONA.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,166,100 Sullinger July 11, 19392,177,416 Alford Oct. 24, 1939 2,183,784 Carter Dec. 19, 1939 2,238,245Brown Apr. 15, 1941 2,240,298 Heindel et al. Apr. 29, 1941 2,251,997Goldmann Aug. 12, 1941 2,255,520 Schuster Sept. 9, 1941 2,268,640 BrownJan. 6, 1942 2,272,608 Hoffman Feb. 10, 1942 2,350,916 Morrison June 6,1944 2,380,519 Green July 31, 1945 2,419,552 I-Iimmel et al Apr. 29,194'? 2,436,843 Watts et al. Mar. 2, 1947

